seamless redundancy concept refinement: duplicate...

2012-11-14 -v02 -

IEEE 802.1 Meeting – San Antonio

Editor:

Franz-Josef Goetz, Siemens AG

Markus Jochim, General Motors

Contributor:

Christian Boiger, University Deggendorf

Oliver Kleineberg, Belden / Hirschmann

Seamless Redundancy Concept Refinement:Duplicate Elimination

IEEE 802.1 Meeting – San Antonio 2012-11-12

Objectives of this Presentation

� Seamless Redundancy concept was presented in San Diego:

http://www.ieee802.org/1/files/public/docs2012/new-avb-kleineberg-jochim-seamless-redundancy-0712

� Joint effort (Industrial Control and Automotive)

� Concept was then discussed in Santa Cruz.

– Some open questions have been identified.

– The group recommended to further refine the concept.

� Intention of this presentation is to do exactly that!


Open Questions Addressed in this Presentation

� Where do we generate and eliminate duplicates?In bridges and in end stations.

� How do we identify duplicates?Based on tagged frames.

� What is the duplicate elimination mechanism?We will present a proposal that is based on a Duplicate Drop Database.


Structure of this Presentation

1. Brief Recap of the Seamless Redundancy Concept

2. Topologies for Redundancy @ Industry & Automotive

3. Mechanism for Seamless Redundancy (based on each other):a) Generation and elimination of duplicates in End Stationsc) Generation and elimination of duplicates in Bridges

4. Concept refinements:a) Mechanism for duplicate elimination

b) Proposed extension of the frame format


Duplication of frame & Redundant paths

B1

B2

B3

B4(E) Sub-System

A

B

CD

F

F’

F

Red = 2-connected part of the network

Orange = disconnecting links

� Each bridge knows (by configuration or by

protocol), which port is connected to a

disconnecting link.

� Within the 2-connected core of the network,

each bridge “knows” two independent paths to

each other bridge.

� Selection of independent paths:

� Required, but not part our work on a Seamless Redundancy Concept.

� The problem is addressed by the Internetworking Group

� Only mission critical frames that enter a bridge via a disconnecting port will be

duplicated and redundantly forwarded on two independent paths.


Elimination of Duplicates

B1

B2

B3

B4(E) Sub-System

A

B

CD

� Bridge B2 “knows”:

1) that the link to B is a Disconnecting Link

AND2) that F and F’ are mission critical frames.

F

F’

FF

� Therefore B2 will eliminate the duplicates and

forward a single copy to B.

� B2 can forward the first copy (F or F’) that arrives.

� B2 does not need to store the first copy that arrives until the other copy arrives!

� B2 just remembers:

“I have seen 1 of the 2 frames already!

If I ever see the other one, I will throw it away!”

� How long will B2 need to remember this?

� Answer: For ∆t = “Max. duration of transmission of F’ from B4 to B2” minus

“Min. transmission duration of F from B4 to B2”


Seamless Redundancy for Reserved and Scheduled Traffic only!

� We propose to provide Seamless Redundancy support for the following traffic

classes:

– Reserved Traffic (Credit based Shaper)

– Scheduled Traffic

� We do not require Seamless Redundancy support for:

– Best Effort Traffic (Strict Priority Scheduling)

� Of course it is NOT REQUIRED to send all reserved traffic or all scheduled traffic

redundantly, but it is POSSIBLE.

� Seamless redundancy can be used for streams that we classify to be mission

critical !


Seamless Redundancy for Reserved and Scheduled Traffic only!

For the rest of the presentation, keep in mind, that whenever we talk

about “frames” or “streams” we will exclusively refer to those

� reserved traffic streams or

� scheduled traffic streams

which have been classified to be mission critical and for which the

seamless redundancy concept shall be applied.


Generation & Elimination of Duplicates

� So far this was just a brief summary of the concept that was presented in

San Diego.

� Note that so far, we exclusively talked about:

� Generation of duplicates in bridges

� Elimination of duplicates in bridges

Within this presentation we will extend the concept to also allow generation and elimination in end stations !


Earth fault introduced

Multiple industrial and automotive use cases have been shown in previous presentations


Redundant Topologies @ Industry

Ring & Coupled Rings:

• Industrial Automation

• Energy Automation

• Rail Systems

• …


Redundant Topologies @ Industry

Parallel Networks:

• Industrial Automation

• Energy Automation

• …

Double Ring

Parallel Network / Dual Homing

... SS ... SS

S S

SS

S S

Ring 1

Ring 2


Redundant Topologies @ Automotive

DG

AS

S

Ethernet

DG DG

FlexRayCANCAN

ECU1& Switch

ECU2& Switch

Camera

Radar

Actuator

Actuator

Ring Structures for robust

backbones

Parallel Networks for safety critical

control applications

or

2 independent channels

(Dual homing)Conclusions:

�Similar topologies in automotive and industry

�Typically larger number of nodes in industry.


How do we implement this?

Information Purpose

VLAN ID • F and F’ are transmitted on independent paths on different VLANs.

• VLAN ID‘s are used to mark redundant path (Path A, Path B, …)

MAC Address • If F and F’ have the same MAC Address, they belong to the same stream.

• A stream MAC address (destination) is unique for VLAN ID‘s used to mark

the redundant path (A, B, …).

Sequence

Number

• A Sequence Number in the frame will enable to identify individual frames

within a stream.

• We are always looking for two frames with the same MAC Address and the

same Sequence number that are transmitted on different VLANs.(This is our assumption, that we need to discuss with the Internetworking Group, since this group is

working on multiple paths.)

� The communication path for Reserved- or Scheduled-Traffic is given by e.g. ISIS-SPB-PCR

� Duplicate elimination requires the ability to identify redundant frames or “frame pairs” (F, F’).

The table gives a high level overview about the information we propose to use for the purpose of

identifying frame pairs:


Generation of duplicates in End Station (Talker T)

For Reserved- or Scheduled Streams

which shall be transmitted over multiple

path End Stations we need to add:

1. VLAN ID for path A or path B and

2. Stream specific Sequence Number

(Redundant streams have identical

Sequence Number for path A and path B)

T talker – single homing

T

Path A

Path B

T

Path APath B

T talker – dual/multiple homing


Elimination of duplicates in End Station (Listener L)

Duplicate Elimination is based on:

� MAC address of Reserved- or Scheduled Streams

� and Sequence Number

Locations for duplicate elimination in end stations:

Single Homing:

� Network Interface

� Network Device Driver

Single & Multiple Homing:

� Application

� Duplicate Elimination Module


Two Examples for Duplicate Generation and Elimination in End Stations

• Reserved- or Scheduled Streams are transmitted over given redundant path

(one common stream for multiple listener)

• Each listener L receives Reserved- or Scheduled Streams twice


Elimination of Duplicates in Bridges (edge port)

L

Path A

Path B

Path A or B

frame path B

frame path A

Path A

Path B

time

Frame path A received before frame path B

When frame path A is correct

-> Forwarding frame path A (no waiting for frame path B)

-> Frame path B will be discarded

in this case

discarding

frame path B

duplicate

elimination

Only one of the duplicates

which are transmitted over

path A or path B will be

received by a listener!

duplicate

elimination

Justification:

• For simple End Stations e.g. sensors with

limited computing power and low power

consumption

• Avoid bandwidth bottleneck on edge port

• Simplify integration of legacy devices

• Network Segment Protection

(To handle one single point of failure in each

network segment, this is very important which

will be explained later)


Two Examples for Duplicate Generation in End Stations and Elimination in Bridges (edge port)


Generation of duplicates in Bridges (1)

Justification:

• For simple End Stations e.g. sensors with

limited computing power and low power

consumption

• Avoid bandwidth bottleneck on edge port

• Simplify integration of legacy devices

• Network Segment Protection

(To handle one single point of failure in each

network segment, this is very important which will

be explained later)


Generation of duplicates in Bridges (2)Network Segments coupled with single Link

Path A

L L

T L

L L

Bridge edge port with

L2 duplicate filtering

network segment 1

network segment 2

Only one Reserved- or Scheduled- path A or B

Frame is forwarded over the link

Path BPath A or B

Bridge port with functionality

adding VLAN ID for path B




adding VLAN ID for path A

Reminder: Bridges do no generate sequence number!

Bridges have to provide functionality to change path A <-> B VLAN ID


Generation of duplicates in Bridges (3)Network Segments coupled with redundant Links

Path A

L L

T L

L L



network segment 1

network segment 2

couple links

Path BPath A or B


adding VLAN ID for path A or path BBridge port with duplicate elimination

and functionality adding VLAN ID for path A or path B

Solution


Generation of duplicates in Bridges (4)Network Segment Protection (1)

L L

T L

Path A

L L

a cb

i j k

g

h

d

m on

s

t

p

u v w

Path A or B

Path BMissing path B

single

point of

failure

Path A

L L

T L

L L

network segment 1

network segment 2

Path B

Path A or B

single

point of

failure

Missing path B

Justification:

A single point of failure within one network segment should not reduce the availability for Reserved- or Scheduled-Traffic in other network segments!


Generation of duplicates in Bridges (5)Network Segment Protection (2)

Path A

L L

T L

L L

network segment 1

network segment 2

Path B

Path A or B

single

point of

failure

Missing path B

single

point of

failure

Missing path A

The Mechanism for segment protection guarantees connectivity!


L2 Duplicate Elimination Mechanism Model (1)

Repetition of our Assumptions:

� Seamless Redundancy only for Reserved- or Scheduled-Traffic (also called stream)

� MAC address (destination address) of Stream is unique

� MAC address & sequence numbers are used for duplicate elimination

Data structure:

� Duplicate-Drop-Window: The size for the window depends on:

� Latency for path A

� Latency for path B

� Transmission period of Reserved- or Scheduled- Stream

T

Path APath B

L Path A or B

latency path A

latency path Bhighest actual

sequence number

Old -> drop frame

Duplicate-Drop-

Window

New -> accept frame

36

20

255 / 0

Sequence Number

68

IEEE 802.1 AVB TG Meeting – San Antonio 2012-10-25

Example for Duplicate Generation & Elimination in Bridges (1)


Proposed Solution: Encapsulation for Duplicate Elimination

Encapsulation for duplicate information:

� TPID : Duplicate Elimination Tag

� Sequence Number : Talker end station have to administrate sequence number stream specific

Requirements:

� Duplicate elimination information shall be protocol neutral (support a wide range of protocols)

� Duplicate elimination per stream (unique destination address)


Discussion of our Proposals

Overview of proposals:

�End Stations and Bridges should be able to generate duplicates.

�End Stations and Bridges should be able to eliminate duplicates.

�A frame format extension was proposed for duplicate identification.

�A duplication elimination mechanism was proposed.

(Keyword: Duplicate Drop Database)

How are we going to proceed?

�We need to agree on a plan…

seamless redundancy concept refinement: duplicate...

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